1. Field of the Invention
The present invention relates generally to punches useful in forming cans from cups and particularly for two piece can forming, and more specifically to such punches that are internally cooled.
2. Brief Description of the Related Art
Forming machines are used to form the bodies of metal containers. A shallow metal cup is driven through a set of annular forming dies by a punch to form the more elongate body of the can, e.g. in a known drawing and ironing process. An example of a conventional can forming machine is shown in U.S. Pat. No. 4,173,882 issued to Lee, Jr. on Nov. 13, 1979, the entire disclosure of which is incorporated herein by reference.
A separate punch typically is removably secured on the leading end of a reciprocating ram in a drawing and ironing machine. The punch provides an inner mandrel on which the can is shaped, drawn, and ironed as it passes through successive dies. The temperature of the punch should be controlled against the heat generated in the punch by repeated frictional contact between the punch, the inside of the can body, and the dies past which the punch moves.
In conventional can formation, externally applied cooling fluids maintain operational temperature conditions. In some can forming applications, however, it is desirable to exclude the conventional use of external cooling fluids. The external cooling fluids may contaminate the container surfaces which would then require post-formation cleaning processes that are costly and may be environmentally undesirable.
Prior arrangements internally cool a punch. U.S. Pat. No. 4,502,313 to Phalin et al., discloses a single coolant inlet passage and a single coolant outlet passage which allow a coolant liquid to flow through a spiral groove adjacent the interior of the punch. U.S. Pat. No. 5,687,604 to Robbins, U.S. Pat. Nos. 5,233,912 and 5,048,592 to Mueller, and U.S. Pat. No. 5,678,442 to Ohba et al. disclose cooling fluid supply and discharge tubes through central conduits. U.S. Pat. No. 6,035,688 to Nagao et al. utilizes a single, continuous passage to supply coolant. The prior art systems are disadvantageous because they do not minimize circumferential direction temperature gradients within the ram and do not provide uniform cooling of the punch.
The present invention overcomes disadvantages of prior art internally cooled punches by supplying fluid, and particularly liquid coolant, through a plurality of annularly arranged fluid transfer tubes to radially arranged ports. Each port feeds into a circumferential channel adjacent the interior surface of the punch that is disposed on and over the end region of the ram inside the punch. The internally cooled punch does not require the use of external cooling fluids. The external temperature of the punch can be monitored continuously, e.g. by direct contact with the punch or by monitoring the temperature of the fluid that cooled the punch, and the cooling fluid medium temperature can be adjusted automatically to maintain acceptable punch temperatures.
Cooling fluid medium is supplied by a temperature control unit and is delivered to the punch through a series of tubes running through the ram. Inlet tubes direct cooling medium toward the distal or leading end of the ram and the punch there. Outlet tubes located more proximally or rearward return the cooling medium out of the punch. Multiple parallel inlet and outlet tubes are spaced circumferentially and symmetrically around the periphery of the punch, with inlet and outlet tubes alternating to distribute the fluid media uniformly around the inner surface of the punch. The multiple fluid inlet and outlet design with symmetrical porting helps assure that the punch temperature remains constant, minimizing circumferential temperature gradients.
Preferably, the fluid transfer tubes are constructed from materials with low thermal transfer properties to minimize heat transfer to the wall of the ram inside the punch. Minimizing heat transfer between the fluid medium and the ram is desirable to maintain accurate fluid heat transfer between the fluid medium and the ram, accurate fluid media inlet temperatures and to minimize ram distortion due to thermal gradients. Circumferential thermal gradients in the ram may distort the ram, adversely altering punch alignment.
Porting between the transfer tubes is circumferentially symmetrical, with alternating inlet and outlet ports, to minimize any circumferential temperature gradients that could transfer to and distort the ram or the surface of the punch. The symmetrically alternating inlet and outlet ports uniformly distribute the fluid medium radially to the inner surface of the punch around the outside of the ram. The transfer tubes also surround a separate central port for air flow and aids that flow in stripping the container from the punch.